1. Field of the Invention
This invention relates to augering machines and further relates to void-creating devices for use in lateral blasting operations. It additionally relates to elevating devices for the boring assembly of an augering machine. It also relates to mining methods that utilize a blast-directing kerf.
2. Review of the Prior Art
Underground mining of coal and other minerals has long been done by cutting a horizontal slot or kerf in the face of a mineral vein to produce a mineral-accepting implosion void therein, boring a plurality of small shot holes into the mineral vein above the kerf and to the same depth as the kerf, inserting explosives into the shot holes, shooting or exploding the explosive to shatter the surrounding mineral and deposit it in the kerf, and removing the broken mineral before repeating the operation. The kerf thus functions as a lateral reaction-directing means so that the force of the explosion is expanded more nearly vertically than outwardly.
Chain-bar cutting machines have been in existence since about 1895 for creating such kerfs in coal seams. Early machines were mounted on rails and could cut to a depth of about four feet under the coal seam. In the early days, bug dust (the flour-size fine coal cuttings) was removed from the kerf so that shooting down the coal was quite effective, particularly when compared to kerfs which were hand-cut with picks and when compared to shooting-on-the-solid (no undercut). Under current practice, this bug dust is not removed.
The basic concept has evolved into the large cutting machines of today which are capable of cutting kerfs having a depth of 10-12 feet. The only major improvement thereover is the universal cutting machine having a cutting boom which can be rotated and raised to approximately 92 inches.
Kerf-cutting machines currently in use are heavy and long (up to 31 feet with boom). A typical machine using alternating current has a 185-horsepower bit motor and a 65-horsepower pump motor. The cutter bar with exposed bits is dangerous and unwieldy. Engineering studies by major mining companies show that 54% of the bug dust remains in a kerf which has been cut by a conventional machine. This unremoved bug dust creates two problems. Firstly, the bug dust creates a cushion which reduces the effectiveness of the shooting and, secondly, the bug dust blows out into the entry and is both an explosion hazard and a respiratory problem. Bug dust is also neither transportable nor saleable.
A slot-like kerf is apparently advantageous from geometry considerations, but the proportion of mineral-receiving void to shattered mineral is low. For example, such a kerf, having a thickness of 4 inches, a width of 20 feet, and a depth of 10 feet, creates a void volume of 67 cubic feet. If a mineral seam is 41/2 feet thick, there are 833 cubic feet of mineral remaining alongside the kerf to be shattered and downwardly expanded toward and into this kerf which provides a mere 8% for such expansion.
On the other hand, if a single cylindrical hole, having a diameter of 2 feet, is bored into the mineral face, there is a void of about 31 cubic feet created in the 900 cubic feet of original mineral. Four such holes, or a single 4 foot diameter hole, have a total void of about 126 cubic feet, furnishing an expansion void equaling about 16% of the remaining mineral or nearly as much as a double cut of 8 inches in thickness.
By cutting one or more cylindrical kerfs with an augering machine, lump coal is automatically extracted therefrom and little dust is created, so that the unsaleability, respiratory and explosive hazards, and cushioning effects of bug dust are eliminated. In addition, the lateral reactive forces created by the explosion are primarily directed sidewardly rather than vertically so that roof damage is minimized. Because roof falls are still the foremost cause of death in coal mining, and indeed were responsible for nearly half the 1973 coal mine deaths, this benefit is alone of considerable importance.
Auger mining machines for mining coal and other minerals from relatively thin veins thereof have been in use for years and have been particularly recommended for mines having poor roof conditions. Such machines comprise a rotary cutting head and a plurality of flights of a spiral conveyor which are sequentially attached in series for boring holes of considerable depth, such as 80 feet to 150 feet. Each flight is generally of a uniform length, such as 6, 10, or 12 feet.
Deep-mine augering machines require an auger elevating means in order to emplace the cutter head at any selected location that is above the floor of the mine entry. An early auger elevating means of the prior art is a rack-and pinion device at each corner of an auger mining machine, as described in U.S. Pat. No. 2,394,194, for elevating the entire machine. Hydraulic jacks, mounted at each corner for separate elevation of the front and rear of the machine in order to compensate for changes in pitch of the seam, were later developed, as described in U.S. Pat. No. 2,880,707.
A deep-mine augering machine, having a rigid anchor frame, a laterally reciprocative sump frame, and a longitudinally reciprocative carriage, is described in copending application Ser. No. 295,511, now U.S. Pat. No. 3,834,761, issued Sept. 10, 1974. In order to bore holes at any elevation in a mineral seam, the entire machine is raised by elevating the underlying anchor frame on the four corner jacks attached thereto. The machine is suggested for use in carrying out a deep-hole method of boring a deep cylindrical kerf to be used for repeated core drilling, shooting, and removing of the shattered coal. An adjacent hole is required for storing auger flights before sequential use thereof.
An arcuately movable and independently operable elevating means is disclosed in U.S. Pat. No. 2,846,093 for a separate transfer mechanism which sequentially removes the auger flights stored in a previously bored hole and transfers them to a nearby auger boring machine which is positioned in front of another hole being bored. This elevating means comprises a rigidly connected pair of side members which are pivotably connected at their lower ends to rollers riding on a pair of rails and have curved seats at their upper ends for supporting an extracted auger flight at a desired elevation.
However, a method of utilizing cylindrical kerfs as expansion voids without requiring an adjacent hole for storage of a large number of bulky, heavy auger flights is clearly needed. For carrying out such a method, a highly maneuverable kerf boring machine having an auger-advancing-and-retracting means and its own independently operable auger elevating means for selectively positioning its auger-boring means without having to elevate the entire machine is equally necessary. Such a machine is best controlled by a seated operator having all hydraulic controls within his reach, but a motionless operator, surrounded by steel in the cold, damp air of a mine, is often chilled for long periods without relief, thereby causing poor posterior circulation and physical aliments. Consequently, an operator warming means is also required.